1. Field of the Invention
The present invention relates to a linear motion guide unit comprised of an elongated guide member such as a track rail or a track shaft, and a slider installed on the guide member for linear movement relative to the guide member by virtue of rolling elements.
2. Description of the Prior Art
In the conventional linear motion guide units, the slider is movable relatively of the guide member such as the track rail or track shaft through the rolling elements of balls or rollers, which are allowed to run through recirculating routes comprised of load areas of raceways defined between grooved or flat surfaces formed on the guide member and grooved or flat surfaces formed in the slider and non-loaded areas including turnarounds and return passages in the slider.
To help ensure the rated durability of the linear motion guide units, it is necessary to keep the rolling elements from metal-to-metal direct contact with the guide surfaces. In addition, the rolling elements have to be certainly lubricated with lubricant supplied always to the recirculating routes. Securing lubrication for the recirculating routes is usually realized by replenishing the recirculating routes with oil at regular intervals.
Recently remarkable needs in reduction of expenditure on maintenance activities as well as in energy savings have given birth to various advanced machines and apparatus, which may operate on maintenance-free. Accordingly, the linear motion guide units are also counted on meeting with needs of maintenance-free. Especially, the linear motion guide units expected incorporated in the semiconductor manufacturing equipment, and so on, which conform the clean-room specifications must meet demands to employ the rolling elements and sliders of specific substances and/or designs that might yield debris or cutting as less as possible when making contact rolling or sliding movement. Moreover, it is inevitable to limit the amount of lubricant used as minimum as possible since fine mist of lubricant might contaminates the atmosphere in the clean room.
A prior linear motion guide unit is disclosed in Japanese Utility Model Laid-Open No. 41724/1989, in which a slider has therein recirculating passages allowing balls to run through them, which are made with self-lubricating members. That is, the self-lubricating members such as oilless metals formed in a tube fit in the recirculating passages to lubricate the balls running through the recirculating passages, rendering the application of lubricant on the slider and track rail unnecessary.
Another conventional linear motion guide unit proposed in Japanese Patent Laid-Open No. 54844/1995 has a slider in which lubricant-containing polymer members are arranged to make rolling contact with the rolling elements, ensuring automatic application of lubricant to the rolling elements over a prolonged period use. The lubricant-containing polymer member is manufactured by the steps of melting the mixture of olefinic polymer with poly (xcex1-olefin) oil or the like, pouring the mixture into a mould and solidifying the molded mixture by cooling under pressure.
Disclosed in Japanese Patent Laid-Open No. 78032/1998 is a lubricant-containing polymer member made of lubricant-containing polymer molded integrally with a reinforcing member.
A further another linear motion guide unit disclosed in Japanese Patent Laid-Open No. 205534/1998, which is comprised of a guide rail made on lengthwise sides thereof with raceway grooves, and a slider fitting over the guide rail for sliding movement relatively of the guide rail, the slider being mounted on forward and aft ends with lubricating plates, one to each end, which are made of sintered resinous components impregnated with lubricant to lubricate the raceway grooves along which rolling elements are allowed to run through.
Although but the prior linear motion guide units recited just above can operate successfully with no application of lubricant when used under light loads in the clean room specifications, they do not always serve well for the recently advanced machinery that has become increasingly higher in speed and oscillation. To produce the lubricant-containing polymer member, any polymer should be molded while being mixed with lubricating oil. In addition, the lubricant-containing polymer member has to be reinforced when incorporated really in the linear motion guide units. To cope with these, highly advanced technology is needed. With the construction in which the lubricating plates are mounted on the slider to make sliding engagement with the track rail, the frictional resistance becomes adversely large when it is applied to machinery high in speed and oscillation.
In the linear motion guide unit where the slider can move linearly along the guide rail by virtue of the rolling elements recirculating through the return passages formed in the slider, thus, it may be worthwhile developing a lubricant applicator member arranged in the return passages to apply the lubricant to the rolling elements, which is improved to have sufficient strength in itself and on itself even with no other reinforcement and continue applying the lubricant to the rolling elements to ensure the smooth travel of the rolling elements over the prolonged period.
The present invention has for its primary object to overcome the problems as described just above, especially provide a linear motion guide unit made free from maintenance such as periodic application and/or suppliance of lubricant: lubricating oil and grease to the guide rail and the rolling elements running through the recirculating route including the guide rail, even under the severe operating conditions in atmosphere and/or subjected load. The linear motion guide unit of the present invention is also less subjected to frictional resistance encountered when the slider moves along the guide rail so that it is well applicable to the high-speed and -oscillation machinery, and makes it possible to realize inexpensive lubrication system.
The present invention is concerned with a linear motion guide unit comprising an elongated guide member, a slider movable lengthwise along the guide member, and rolling elements allowed to run through a recirculating route including a load raceway defined between the guide member and the slider, a turnaround formed in the slider to communicate with the load raceway, and a return passage formed in the slider to communicate with turnaround, wherein the return passage is encircled with a sintered resinous member of porous texture, which can be impregnated with lubricant.
In accordance with an aspect of the present invention, a linear motion guide unit is disclosed wherein the sintered resinous member is made of sintered porous polymer. Moreover, the sintered resinous polymer is produced by filling a preselected mould with powdery ultrahigh molecular weight synthetic resin, and then heating the molded resin under high pressure. This form of production makes it possible to prepare the sintered resinous member inexpensively and in mass-production techniques.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the powdery synthetic resin is composed of at least one substance selected from polyethylene, polypropylene and tetrafluoroethylene polymer. The powdery ultrahigh molecular weight polyethylene is a material preferable for producing the molded article with high accuracy and further the resultant sintered resinous members are superior in wear proof.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the sintered resinous member is formed in a sleeve, which fits in a bore in the slider to form the return passage.
In accordance with a further another aspect of the present invention, a linear motion guide unit is disclosed wherein the sleeve is made by rolling up a sheet of the sintered resinous member. Alternatively, the sleeve may be made of a pair of halves of the sintered resinous member, which are matched together with each other. Moreover, the sintered resinous member surrounding around the return passage may be made in a block to form a part of the slider. In this later embodiment, the return passage has a diameter enough to allow the rolling elements to run through there while the bore in the slider has a diameter that is determined in consideration of both the diameter of the return passage and the thickness of the sleeve construction. As the sleeve constructions stated earlier can be all formed without using a core, the sintered resinous member can be formed and worked much easier to make it possible to prepare the return passage with ease.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the sintered resinous member defining the return passage is provided therein with a lubricant reservoir having any shape selected from a recess, a slit and a groove. The lubricant reservoir in the sintered resinous member makes it easy to hold excess amount of lubricant, which may be supplied little by little over a prolonged period to the rolling elements.
In accordance with another aspect of the present invention, a linear motion guide unit is disclosed wherein the guide member is a track rail made on lengthwise sides thereof with first raceway grooves to provide the load raceways, the slider is formed so as to fit astride over and conform to the track rail for movement relatively of the track rail, the slider being comprised of a casing having second raceway grooves confronting the first raceway grooves to define the load raceways between them, and end caps mounted on forward and aft ends of the casing, and the return passages are formed in the casing while the turnarounds are formed in the end caps. With this linear motion guide unit stated just above, the rolling elements employed are balls.
In another aspect of the present invention, a linear motion guide unit is disclosed wherein the guide member is a track shaft provided on radially opposing sides thereof with lengthwise first raceway grooves, and the slider is formed in a hollow cylinder, which fits over the track shaft for movement relatively of the track shaft, the slider being comprised of a casing having second raceway grooves confronting the first raceway grooves to define the load raceways between them, and end caps mounted on forward and aft ends of the casing, and the return passages are formed in the casing while the turnarounds are formed in the end caps. This modification also uses the rolling elements of balls.
In a further aspect of the present invention, a linear motion guide unit is disclosed wherein the guide member is a track rail made on lengthwise sides thereof with first raceway grooves to provide the load raceways, the slider is comprised of a casing having second raceway grooves confronting the first raceway grooves to define the load raceways between them, and end caps mounted on forward and aft ends of the casing, the rolling elements are rollers, and the return passages are formed in the casing while the turnarounds are formed in the end caps.
With the linear motion guide units constructed as stated earlier, the sintered resinous member has the porous texture capable of keeping the lubricant therein. Thus, the lubricant such as grease, oils, and so on charged once into the sintered resinous member when assembled is absorbed and held in voids in the sintered resinous member, and thereafter supplied continually to the rolling elements running through the return passage.
That is to say, the lubricant in the porous texture of the sintered resinous member is consumed transferred little by little to the rolling elements when making contact with the rolling elements. The lubricant adhered on the rolling elements is then applied to the raceways as the rolling elements run through the raceways. When the rolling elements entraining lubricant thereon run through the load raceways defined between the confronting guide member and slider, lubrication is realized on the load raceways and raceway grooves. The sintered resinous member of porous texture has the property capable of absorbing not only oily content but also other specific contents such as fine powdery solid lubricant, fine powdery coating material and other additives. The sintered resinous member has sufficient strength in itself and on itself even with no other reinforcement. Moreover, the sintered resinous member used in the present invention, as being less subjected to wear, is tough to clogging, which might be caused by cuttings, debris, and so on occurring due to wear, thereby to make it possible to continue applying over a prolonged period the lubricant, which is stored in the porous texture, to the rolling elements. Thus, even under the operating conditions where the atmosphere has a high temperature or the lubricant is extremely less in admitted amount, the sintered resinous member serves well to eliminate the metal-to-metal contact of the rolling elements with the raceways or passages, improving the lubricating property, thereby ultimately increasing the durability of the linear motion guide unit. Alternatively, it is permitted to impregnate the sintered resinous member with lubricant prior to assembling it with the slider.
The linear motion guide unit of the present invention is made free from maintenance such as periodic application and/or suppliance of lubricant, and reduced in frictional resistance encountered at the raceways when the slider moves along the guide member. This improved linear motion guide unit can be even used for the advanced machinery operated on high-speed and-oscillation.
Other aspect and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.